1. Field of the Invention
The present invention relates to an image forming apparatus and method, and more particularly to an image forming apparatus and an image forming method which forms images on a recording medium by discharging ink from an inkjet head. Furthermore, the present invention relates to an image forming apparatus and an image forming method suitable for forming color images by discharging inks of a plurality of colors onto a recording medium by means of full line type inkjet heads having a nozzle row spanning a length corresponding to the entire printable width.
2. Description of the Related Art
There is an inkjet type image forming apparatus using ultraviolet curable ink (so-called UV ink). Japanese Patent Application Publication No. 2002-347232 discloses a technology comprising a heating unit for heating the ink provided between a full line type recording unit which discharges light-curable ink, and a light irradiating section for irradiating UV light for curing ink, onto ink that has been discharged onto a recording medium. The evaporation of the ink solvent is accelerated by the heating unit, and hence the speed of the curing speed of the ink becomes faster.
However, the action of the heating unit disclosed in Japanese Patent Application Publication No. 2002-347232 contributes to the evaporation of the ink solvent, while making little contribution to curing of the ink. Therefore, even if a heating unit is disposed immediately after each head, as illustrated in FIG. 7 of Japanese Patent Application Publication No. 2002-347232, droplets are still ejected from a subsequent (downstream) head while the ink discharged from an upstream head is in a liquid state on the recording medium, and hence there is interference between droplets on the surface of the recording medium, and bleeding of the colors due to color mixing. Consequently, image quality declines.
Japanese Patent Application Publication No. 2003-11341 discloses that an active light beam be irradiated within 10 seconds of the discharge of all inks required to form an image, when using inks of a plurality of colors. This composition is, however, for irradiating an activating light beam after inks of all of the required colors for image formation have been ejected, and therefore, similarly to Japanese Patent Application Publication No. 2002-347232, color bleeding occurs due to mixing of the colors.
Japanese Patent Application Publication No. 2003-127517 discloses that, after spraying ink droplets onto a recording medium, ultraviolet light having a wavelength of 340 to 400 nm is irradiated for 0.1 to 10 seconds, whereupon ultraviolet light having a wavelength of 280 to 400 nm is irradiated for 10 to 1000 seconds. Japanese Patent Application Publication No. 2003-127517 discloses that light is irradiated from a curing light source by dividing the wavelength range and the irradiation time of the curing light source into two stages; however, it does not disclose the positional relationship between the head and the irradiation light source, and it is unclear at what timing the irradiation of light is actually performed.
Japanese Patent Application Publication No. 2003-191594 discloses that a device is provided in order to vary the irradiation conditions of an activating light beam, as desired, after ink has been deposited. Japanese Patent Application Publication No. 2003-191594 describes varying the irradiation conditions of the activating light source, namely, the irradiation time, the irradiation timing, the irradiation intensity, the irradiation energy, the type of light source, the irradiation surface area, the angle of incidence, and the wavelength characteristics; however, it does not disclose a composition for the apparatus which indicates the positional relationship between the irradiation light source and the head, and it is unclear what kind of device (apparatus) is used to achieve this.
Japanese Patent Application Publication No. 2003-182048 discloses a method for forming images by creating print data in such a manner that there is no mutual interference between adjacently positioned dots on the recording medium, and repeating an operation of printing (discharging ink) and an operation of ultraviolet curing, on the basis of the print data. Japanese Patent Application Publication No. 2003-182048 forms an image progressively by repeating the operations of a print section and an ultraviolet curing section, and therefore it is difficult to achieve high-speed output. Furthermore, Japanese Patent Application Publication No. 2003-182048 does not describe the positional relationship between the head and the UV irradiation device.
Japanese Patent Application Publication No. 2003-11343 discloses a composition for a shuttle scan type inkjet recording apparatus which forms images by moving a recording head reciprocally, in which the deposition of ink onto the recording medium is divided into a plurality of actions based on the reciprocal movement of the recording head, and ultraviolet light is irradiated between each deposition action. Japanese Patent Application Publication No. 2003-11343 states that ink is fixed by irradiation of ultraviolet light between the respective ink deposition actions performed by a shuttle scanning type of system, and the amount of light irradiated must be sufficient to fix the ink. However, if ultraviolet light of an amount required to fix the ink is irradiated in the vicinity of the head, then the ink inside the nozzle is hardened by the random reflection from the print medium, and the like, and this can lead to discharge errors.
Japanese Patent Application Publication No. 2001-1512 discloses an inkjet printer comprising an image forming section which discharges ink onto paper in sheet form (print object) and a pressurizing section which pressurizes the printing object formed with an image by the image forming section. This printer is composed in such a manner that a gloss finish is applied to the image by pressurizing and flattening the surface undulations of the ink on the image formed on the print object by the image forming section. Japanese Patent Application Publication No. 2001-1512 is a technology which assumes that a pigment-based ink or dye-based ink is used as the printing ink. However, technology using ultraviolet curable type ink is known in inkjet type image forming apparatuses. Various merits are obtained by using an ultraviolet curable ink, namely, images can be formed onto recording media of various types and hence the recording medium can be selected from a wide range, and the like. However, if an ultraviolet curable ink is used within the technical scope described in Japanese Patent Application Publication No. 2001-1512, problems arise in that fracturing and peeling occurs in the ink surface when the ink is flattened by pressurization.